Polyalkenyl substituted mono- and dicarboxylic acid producing materials, most notably polyisobutenyl succinic acids and anhydrides, are known intermediates for the preparation of products useful as additives in lubricants, fuels, and functional fluids. In particular, succinamide and succinimide products produced by the reaction of monoamines or polyamines with polyalkenyl succinic anhydrides have been employed as ashless dispersants and detergent additives in lubricating oils and in fuels. Succinic esters produced by the reaction of monoalcohols or polyols with polyalkenyl succinic anhydrides have also been used as ashless dispersants and detergents.
Polyalkenyl substituted mono- and dicarboxylic acid producing materials have been prepared using a one-step chloro process in which a polyalkene and an unsaturated mono- or dicarboxylic acid producing compound are reacted at elevated temperature in the presence of chlorine. The polyalkenyl mono- or dicarboxylic acid materials have also been prepared using a two-step chloro process in which the polyalkene is chlorinated in the first step and the resulting chlorinated polyalkene is then reacted with the unsaturated mono- or dicarboxylic compound at elevated temperature. The one- and two-step chloro processes can produce polyalkenyl substituted mono- or dicarboxylic acid materials in relatively high yields and without the formation of substantial amounts of sediments and other undesirable byproducts. On the other hand, these products typically contain residual chlorine, and environmental concerns related to chlorine-containing materials make the use of the chloro processes undesirable.
The polyalkenyl substituted carboxylic materials can also be prepared by the direct thermal reaction of a polyalkene and an unsaturated mono- or dicarboxylic acid compound, often referred to in the art as the thermal ene process. While the thermal ene process has the advantage of avoiding the use of chlorine, the reaction tends to proceed only slowly and with low yields at reaction temperatures below about 150.degree. C. At higher reaction temperatures, the thermal ene process typically has better yields, but it also tends to produce significant amounts of a sediment byproduct which must be filtered from the final product prior to its use as an additive or intermediate. The process also tends to produce tars, which coat the reactor walls, necessitating frequent, time-consuming, and therefore costly clean-ups of the reactor vessel. These sediments and tars are believed to be due at least in part to the decomposition and/or polymerization of the unsaturated mono- or dicarboxylic acid compound, which has typically been maleic anhydride.
Additives can be employed in the thermal ene reaction in order to reduce the formation of tars and sediments. For example, U.S. Pat. No. 4,235,786 discloses that sediment formation in the ene reaction can be markedly reduced by the presence of a sediment-reducing amount of an oil-soluble strong organic acid. The patent discloses that the oil-soluble strong organic acid is preferably a C.sub.15 -C.sub.70 optimally C.sub.28 -C.sub.36 hydrocarbyl substituted sulfonic acid. Example 1 discloses that a polyisobutylene having a number average molecular weight ("M.sub.n ") of 900 was reacted with maleic anhydride at 235.degree. C. for 6 hours under a pressure maintained at about 150 kPa in the presence of an alkylated benzene sulfonic acid having M.sub.n of 500 and containing an average of about total 30 carbons. The resulting product had 0.2% sediment. The procedure of Example 1 was followed in Example 2 except that no sulfonic acid was present. The resulting product had 3.0% sediment, based upon which the patent discloses that it is apparent that the presence of about 0.13 wt.% of an acid reduced the sediment formation by 93%.
Improved thermal ene processes utilizing polyalkene reactants having a relatively high proportion of terminal double bonds have also been disclosed. Terminal double bonds, particularly terminal vinylidene bonds, in polyalkenes are recognized to be generally more reactive in the thermal ene process than internal double bonds. U.S. Pat. No. 4,152,499, for example, discloses that adduct formation between maleic anhydride and polyisobutene virtually only occurs between maleic anhydride and a terminal double bond. U.S. Pat. No. '499 further discloses that double bonds in the .beta. position are also capable of reacting to a certain degree, while virtually no reaction occurs at double bonds further removed from the chain ends. U.S. Pat. No. 4,086,251 discloses that terminal vinylidene is believed to be the most reactive of the terminal double bonds in polybutenes. Conventional polyisobutenes, formed by cationic polymerization using aluminum chloride catalysts such as AICI.sub.3, generally have a relatively low content of terminal double bonds. Polyisobutenes having a high content of terminal double bonds, so-called "reactive" polyisobutenes, have been achieved by BF.sub.3 -catalyzed polymerization of isobutene. Other polyalkenes having a high content of terminal double bonds (e.g., ethylene-.alpha.-olefin copolymers and .alpha.-olefin homo- and copolymers) have been disclosed to be prepared by polymerization of the corresponding monomers in the presence of metallocene catalyst systems.
The improved thermal ene processes utilizing these more reactive polyalkenes have been disclosed to provide products with low sediment and/or low tar. For example, U.S. Pat. No. 5,071,919 discloses a process for preparing substituted succinic acylating agents by reacting an acidic reactant such as maleic anhydride with a substantially aliphatic polymer comprised principally or entirely of polyisobutenes in a mole ratio of acidic reactant:polymer of at least 1:1, provided that at least 50% of the polyisobutene content of the polymer has terminal vinylidene end groups and the reaction is maintained under superatmospheric pressure during at least a substantial portion of the reaction period. The patent discloses that reaction product mixtures formed by this process contain little or no tars. Another example is U.S. Pat. No. 5,229,022 which discloses the thermal ene reaction of ethylene-.alpha.-olefin polymers having a high terminal ethenylidene (i.e., vinylidene) content with monounsaturated carboxylic reactants. The patent discloses that the ethylene-.alpha.-olefin polymers readily undergo thermal ene reactions under conditions in which the formation of sediment or other byproducts contributing to product haze is greatly minimized or avoided altogether. It is further disclosed that the resulting ene reaction product mixture can be employed, without filtering, centrifuging, clarification, phase separation or other conventional product purification treatments.
There is a continuing need for the development of improved thermal ene processes. In particular, while prior art processes employing tar suppressants and sediment inhibitors have reduced the amount of sediments and/or tars, they have not generally not eliminated their formation, particularly as applied to polyalkenes having a low content of terminal vinylidene polymer chains. Accordingly, the products resulting from these processes still typically require treatment to remove sediments and the reaction vessels must still be cleaned regularly to remove tars.